The present invention relates generally to image processing systems and, more particularly, to methods and devices for generating, viewing, editing and validating profiles linking different transform spaces. In a particularly useful embodiment, the profiles are generated between first and second color spaces where one of the color spaces is associated with either a source or a destination device in an image processing system. The profile can then be utilized within image processing software, or the contents of the profile can be viewed, edited or validated.
Digital image processing involves electronically capturing an image of a scene, altering the captured image in some desired fashion and passing the altered image to an output device. An upstream element of a digital image processing system can be thought of as a source device, whereas a downstream element can be thought of as a destination device. For instance, a simple image processing system could include an image acquisition device such as a digital camera, camcorder, scanner, CCD, etc., a color processor for processing the colors of the image, and an image rendering device, such as a printer, monitor, computer memory, etc. When considering a communication between the acquisition device and image rendering device, the acquisition device is deemed as the source device whereas the image rendering device is deemed as the destination device. All imaging devices impose distortions on both the color and other characteristics of an image.
Transferring images and documents between digital imaging devices such as monitors, scanners and printers requires color matching, i.e. matching of color characteristics of the respective devices since different imaging devices have different color capabilities, describe color characteristics in different terms, and operate in different color spaces. For example, a color display monitor in a computer system may operate in RGB color space by creating and describing colors in terms of red, green and blue (RGB) values. The RGB values associated with particular colors for the display monitor are device-dependent in that the RGB values associated with specific colors are particular for the given monitor. Since the RGB values are device-dependent, colors displayed on different monitors will probably not be visually identical even for the same RGB input values.
Most printers create and describe colors in device-dependent terms differing from those used by monitors. For example, printers use cyan magenta, yellow and black (CMYK) values to describe colors, and are said to operate in the CMYK color space. Since the CMYK values are device-dependent, colors printed on any given printer will probably not match colors printed on a different printer for the same CMYK value.
Further complicating color matching between devices is the fact that different devices have different color capabilities. Every rendering device, such as a printer or monitor, has a limited range of colors, i.e. a gamut, that it can reproduce. Those skilled in the art will recognize that color display monitors tend to be able to produce a wider range of lighter colors whereas color printers tend to be able to produce a wider range of darker colors. Consequently, the gamut for a color display monitor is different from the gamut for a color printer. As a result, some colors displayed on display monitors cannot be reproduced on color printers and vice versa.
Models are often used to translate colors between devices while trying to maintain the perceived color appearance. For example, suppose that the user displays an image on a monitor. If he prints the image without any color matching, the color appearance of the printed image will differ significantly from that of the original. Using a color matching model, this difference can be reduced to a perceptively acceptable level. Color matching models can be empirically or analytically derived.
In recent years, device-independent paradigms for the characterization of color information in an image processing system have been developed and are being implemented. ColorSync, developed by Apple Computer and KCMS, developed by Eastman Kodak Co., are examples of systems or components supporting a device-independent color paradigm. This paradigm is based upon a characterization of the image pixel data (digits) in a device-independent color space, e.g. CIE L*a*b* or CIE XYZ, using a color management system.
U.S. Pat. No. 5,561,459 issued Oct. 1, 1996 to Stokes et al. discloses automatic profile generation for a self-calibrating color display. Cathode ray tube (CRT) parameters are measured and combined with previously acquired calibration parameters in order to create updated characteristic information for the profile. The characteristic information includes the CRT color gamut, the white and black point of the CRT and the gamma of the CRT. In addition, ambient lighting conditions may be included in the profile. This characteristic information is stored in a CRT characterization profile in a standardized format. The profile is updated whenever the CRT is recalibrated or whenever the operating conditions of the CRT are changed. Further, the profile may be employed to recalibrate a destination CRT based on a source CRT's profile.
U.S. Pat. No. 5,612,902 issued Mar. 18, 1997 to Stokes discloses a system and method for automatic characterization of a color printer using an analytical model which, in turn, is used to generate a multidimensional lookup table which can be used at runtime to compensate image input and create desired visual characteristics in the printed image. A detector can be incorporated into the printer which measures at least one parameter of each printed sample so that characterization can be carried out internally to the printer in a manner which is transparent to the end user. In this way, changes in paper stock, inks, or environment can be custom compensated for each printing application.